Avoid getting tainted? What does that even mean.

Avoid reading the code, being inpired by it and using the same pattern (or worse, snippets) in your project (which could result in legal actions against you).

I have often heard it in the context of windows operating system developper which should be careful of not accidently introducing open-source code in the kernel if it might have a license that is not compatible with Microsoft's one.

There’s no law against that unless you’re implementing a patented algorithm, which is dumb in any case.

Alternative implementations of programs often use Clean Room reverse engineering, for a reason.

What if you copy paste code that is under a viral license ?

If you read the code and work in the same field, you may inadvertently implement some feature in a very similar way. That might lead to lawsuits.

That's why CodeWeavers, which partners with Valve, when hiring developers for Proton/WINE states as a requirement:

> No exposure to Microsoft code or reverse-engineering of Microsoft software

Ref https://www.codeweavers.com/about/jobs